Power Valve Restrictor Channel Tuning

[Ivoryk3ys78]

Good Afternoon.

I have a proform race carb and a wideband 02 sensor. I am going to dial in the jetting for lean cruise and WOT. I would like to be able to enrich the power valve circuit more and Proform and other billet metering block style carbs have screw in jets so that you can adjust how much it enriches. My understanding are that these are 6-32 air bleeds.

My problem is I can not find different size jets for it anywhere. I can find small idle air bleeds but nothing in the diameter that you would use for power valve restrictors. I can find screw in blanks that you can drill but boy that would be some awful small drilling.

Any ideas on this would be appreciated.

Thank you

 

[Mattax]

Good Afternoon.

I have a proform race carb and a wideband 02 sensor. I am going to dial in the jetting for lean cruise and WOT. I would like to be able to enrich the power valve circuit more and Proform and other billet metering block style carbs have screw in jets so that you can adjust how much it enriches. My understanding are that these are 6-32 air bleeds.

My problem is I can not find different size jets for it anywhere. I can find small idle air bleeds but nothing in the diameter that you would use for power valve restrictors. I can find screw in blanks that you can drill but boy that would be some awful small drilling.

Any ideas on this would be appreciated.

Thank you

Air bleeds are for getting the AFR so its flat through the top of the run. They also can effect how smoothly the main circuit initiates but that's secondary.

The power valve channel restrictors control the amount of enrichment fuel. Think of them as an additional main jet.
If your carb's metering blocks have threaded PVCRs, then BLP or Quick Fuel or Proform should have them.
Yes the alternative is to drill your own.
There are other work arounds. To my surprise I have found the PCVR on an old holley was exactly the right size. Of the two best jettings on the chassis dyno, the leaner was just past what the engine would tolerate at highway speeds. That worked out well 'cause at the track I would have chosen the richer of the two anyway.

 

[Ivoryk3ys78]

Thank you.

Yeah I been reading though David Vizards Holley Super Tuning book. He goes into how the high speed air bleeds can be used to shape the curve in the upper rpm range.

I think I found what I need finally! On summit I was able to find from Quick fuel idle Feed Restrictors all 6-32. So you can't find anything listed as PVCR except for blanks but if you search for idle feed trstrictors you can find a lot of sizes that seem to cover the right range and from what I understand those should screw right in.
Not an easy thing to find. I asked for summit tech support and the guy gets on the phone and tells me that I don't understand how it works and I don't want to restrict the power valve and then goes into how the power valve works.

A little humility is always a good thing. You never know when a subject will come up that you don't know anything about.

Air bleeds are for getting the AFR so its flat through the top of the run. They also can effect how smoothly the main circuit initiates but that's secondary.

The power valve channel restrictors control the amount of enrichment fuel. Think of them as an additional main jet.
If your carb's metering blocks have threaded PVCRs, then BLP or Quick Fuel or Proform should have them.
Yes the alternative is to drill your own.
There are other work arounds. To my surprise I have found the PCVR on an old holley was exactly the right size. Of the two best jettings on the chassis dyno, the leaner was just past what the engine would tolerate at highway speeds. That worked out well 'cause at the track I would have chosen the richer of the two anyway.

 

[Mattax]

Off the top of my head, I recall one of my Holleys has a .050" PVCR. I can look at some others but probably what will help you is just seeing what is in your carb to start with. You can use the back of a drill bit as a cheap pin gage.

 

[Ivoryk3ys78]

The way I plan on adjusting it is to tune the primary jets to get the lean cruise numbers I want. Put a power valve block in and square the jets and find the WOT numbers I want. Set the primary back to cruise jets and install the power valve and richen PVCR until WOT levels are reached again. Adjust high speed air bleeds if need to be adjust WOT curve. Deal with any accelerator pump issues that might arise.

I called Proform to find out what was in the PVCR ( I am thinking it will be about .040) but was told they had no one in the shop because of this Wuhan virus bs. Thanks for the tip on the drill bit.